From: Szabolcs Nagy Date: Tue, 4 Jul 2017 15:05:12 +0000 (+0100) Subject: Single threaded stdio optimization X-Git-Tag: glibc-2.26~153 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d2e04918833d90bae7fe5410bb70a045bbd2b64d;p=thirdparty%2Fglibc.git Single threaded stdio optimization Locking overhead can be significant in some stdio operations that are common in single threaded applications. This patch adds the _IO_FLAGS2_NEED_LOCK flag to indicate if an _IO_FILE object needs to be locked and some of the stdio functions just jump to their _unlocked variant when not. The flag is set on all _IO_FILE objects when the first thread is created. A new GLIBC_PRIVATE libc symbol, _IO_enable_locks, was added to do this from libpthread. The optimization can be applied to more stdio functions, currently it is only applied to single flag check or single non-wide-char standard operations. The flag should probably be never set for files with _IO_USER_LOCK, but that's just a further optimization, not a correctness requirement. The optimization is valid in a single thread because stdio operations are non-as-safe (so lock state is not observable from a signal handler) and stdio locks are recursive (so lock state is not observable via deadlock). The optimization is not valid if a thread may be created while an stdio lock is taken and thus it should be disabled if any user code may run during an stdio operation (interposed malloc, printf hooks, etc). This makes the optimization more complicated for some stdio operations (e.g. printf), but those are bigger and thus less important to optimize so this patch does not try to do that. * libio/libio.h (_IO_FLAGS2_NEED_LOCK, _IO_need_lock): Define. * libio/libioP.h (_IO_enable_locks): Declare. * libio/Versions (_IO_enable_locks): New symbol. * libio/genops.c (_IO_enable_locks): Define. (_IO_old_init): Initialize flags2. * libio/feof.c.c (_IO_feof): Avoid locking when not needed. * libio/ferror.c (_IO_ferror): Likewise. * libio/fputc.c (fputc): Likewise. * libio/putc.c (_IO_putc): Likewise. * libio/getc.c (_IO_getc): Likewise. * libio/getchar.c (getchar): Likewise. * libio/ioungetc.c (_IO_ungetc): Likewise. * nptl/pthread_create.c (__pthread_create_2_1): Enable stdio locks. * libio/iofopncook.c (_IO_fopencookie): Enable locking for the file. * sysdeps/pthread/flockfile.c (__flockfile): Likewise. --- diff --git a/ChangeLog b/ChangeLog index 314c69f6645..7f67b658f3e 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,21 @@ +2017-07-04 Szabolcs Nagy + + * libio/libio.h (_IO_FLAGS2_NEED_LOCK, _IO_need_lock): Define. + * libio/libioP.h (_IO_enable_locks): Declare. + * libio/Versions (_IO_enable_locks): New symbol. + * libio/genops.c (_IO_enable_locks): Define. + (_IO_old_init): Initialize flags2. + * libio/feof.c.c (_IO_feof): Avoid locking when not needed. + * libio/ferror.c (_IO_ferror): Likewise. + * libio/fputc.c (fputc): Likewise. + * libio/putc.c (_IO_putc): Likewise. + * libio/getc.c (_IO_getc): Likewise. + * libio/getchar.c (getchar): Likewise. + * libio/ioungetc.c (_IO_ungetc): Likewise. + * nptl/pthread_create.c (__pthread_create_2_1): Enable stdio locks. + * libio/iofopncook.c (_IO_fopencookie): Enable locking for the file. + * sysdeps/pthread/flockfile.c (__flockfile): Likewise. + 2017-07-04 Florian Weimer [BZ #21542] diff --git a/libio/Versions b/libio/Versions index 2a1d6e6c852..77123347e3c 100644 --- a/libio/Versions +++ b/libio/Versions @@ -155,5 +155,8 @@ libc { GLIBC_PRIVATE { # Used by NPTL and librt __libc_fatal; + + # Used by NPTL + _IO_enable_locks; } } diff --git a/libio/feof.c b/libio/feof.c index 9712a81e783..8890a5f51fe 100644 --- a/libio/feof.c +++ b/libio/feof.c @@ -32,6 +32,8 @@ _IO_feof (_IO_FILE *fp) { int result; CHECK_FILE (fp, EOF); + if (!_IO_need_lock (fp)) + return _IO_feof_unlocked (fp); _IO_flockfile (fp); result = _IO_feof_unlocked (fp); _IO_funlockfile (fp); diff --git a/libio/ferror.c b/libio/ferror.c index 01e3bd8e2b8..d10fcd9fff2 100644 --- a/libio/ferror.c +++ b/libio/ferror.c @@ -32,6 +32,8 @@ _IO_ferror (_IO_FILE *fp) { int result; CHECK_FILE (fp, EOF); + if (!_IO_need_lock (fp)) + return _IO_ferror_unlocked (fp); _IO_flockfile (fp); result = _IO_ferror_unlocked (fp); _IO_funlockfile (fp); diff --git a/libio/fputc.c b/libio/fputc.c index a7cd682fe2b..b72305c06f1 100644 --- a/libio/fputc.c +++ b/libio/fputc.c @@ -32,6 +32,8 @@ fputc (int c, _IO_FILE *fp) { int result; CHECK_FILE (fp, EOF); + if (!_IO_need_lock (fp)) + return _IO_putc_unlocked (c, fp); _IO_acquire_lock (fp); result = _IO_putc_unlocked (c, fp); _IO_release_lock (fp); diff --git a/libio/genops.c b/libio/genops.c index a466cfa3370..6ad7346cae5 100644 --- a/libio/genops.c +++ b/libio/genops.c @@ -570,11 +570,39 @@ _IO_init (_IO_FILE *fp, int flags) _IO_init_internal (fp, flags); } +static int stdio_needs_locking; + +/* In a single-threaded process most stdio locks can be omitted. After + _IO_enable_locks is called, locks are not optimized away any more. + It must be first called while the process is still single-threaded. + + This lock optimization can be disabled on a per-file basis by setting + _IO_FLAGS2_NEED_LOCK, because a file can have user-defined callbacks + or can be locked with flockfile and then a thread may be created + between a lock and unlock, so omitting the lock is not valid. + + Here we have to make sure that the flag is set on all existing files + and files created later. */ +void +_IO_enable_locks (void) +{ + _IO_ITER i; + + if (stdio_needs_locking) + return; + stdio_needs_locking = 1; + for (i = _IO_iter_begin (); i != _IO_iter_end (); i = _IO_iter_next (i)) + _IO_iter_file (i)->_flags2 |= _IO_FLAGS2_NEED_LOCK; +} +libc_hidden_def (_IO_enable_locks) + void _IO_old_init (_IO_FILE *fp, int flags) { fp->_flags = _IO_MAGIC|flags; fp->_flags2 = 0; + if (stdio_needs_locking) + fp->_flags2 |= _IO_FLAGS2_NEED_LOCK; fp->_IO_buf_base = NULL; fp->_IO_buf_end = NULL; fp->_IO_read_base = NULL; diff --git a/libio/getc.c b/libio/getc.c index b58fd623086..fd66ef93cf4 100644 --- a/libio/getc.c +++ b/libio/getc.c @@ -34,6 +34,8 @@ _IO_getc (FILE *fp) { int result; CHECK_FILE (fp, EOF); + if (!_IO_need_lock (fp)) + return _IO_getc_unlocked (fp); _IO_acquire_lock (fp); result = _IO_getc_unlocked (fp); _IO_release_lock (fp); diff --git a/libio/getchar.c b/libio/getchar.c index 5b41595d17f..d79932114ee 100644 --- a/libio/getchar.c +++ b/libio/getchar.c @@ -33,6 +33,8 @@ int getchar (void) { int result; + if (!_IO_need_lock (_IO_stdin)) + return _IO_getc_unlocked (_IO_stdin); _IO_acquire_lock (_IO_stdin); result = _IO_getc_unlocked (_IO_stdin); _IO_release_lock (_IO_stdin); diff --git a/libio/iofopncook.c b/libio/iofopncook.c index a08dfdaa425..982f464a685 100644 --- a/libio/iofopncook.c +++ b/libio/iofopncook.c @@ -172,6 +172,8 @@ _IO_cookie_init (struct _IO_cookie_file *cfile, int read_write, _IO_mask_flags (&cfile->__fp.file, read_write, _IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING); + cfile->__fp.file._flags2 |= _IO_FLAGS2_NEED_LOCK; + /* We use a negative number different from -1 for _fileno to mark that this special stream is not associated with a real file, but still has to be treated as such. */ diff --git a/libio/ioungetc.c b/libio/ioungetc.c index 951064fa127..917cad8abb2 100644 --- a/libio/ioungetc.c +++ b/libio/ioungetc.c @@ -33,6 +33,8 @@ _IO_ungetc (int c, _IO_FILE *fp) CHECK_FILE (fp, EOF); if (c == EOF) return EOF; + if (!_IO_need_lock (fp)) + return _IO_sputbackc (fp, (unsigned char) c); _IO_acquire_lock (fp); result = _IO_sputbackc (fp, (unsigned char) c); _IO_release_lock (fp); diff --git a/libio/libio.h b/libio/libio.h index 518ffd8e44f..14bcb92332c 100644 --- a/libio/libio.h +++ b/libio/libio.h @@ -119,6 +119,7 @@ # define _IO_FLAGS2_SCANF_STD 16 # define _IO_FLAGS2_NOCLOSE 32 # define _IO_FLAGS2_CLOEXEC 64 +# define _IO_FLAGS2_NEED_LOCK 128 #endif /* These are "formatting flags" matching the iostream fmtflags enum values. */ @@ -451,6 +452,9 @@ extern int _IO_ftrylockfile (_IO_FILE *) __THROW; #define _IO_cleanup_region_end(_Doit) /**/ #endif +#define _IO_need_lock(_fp) \ + (((_fp)->_flags2 & _IO_FLAGS2_NEED_LOCK) != 0) + extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict, _IO_va_list, int *__restrict); extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict, diff --git a/libio/libioP.h b/libio/libioP.h index eb93418c8d3..1832b44cc7f 100644 --- a/libio/libioP.h +++ b/libio/libioP.h @@ -444,6 +444,8 @@ extern void _IO_list_unlock (void) __THROW; libc_hidden_proto (_IO_list_unlock) extern void _IO_list_resetlock (void) __THROW; libc_hidden_proto (_IO_list_resetlock) +extern void _IO_enable_locks (void) __THROW; +libc_hidden_proto (_IO_enable_locks) /* Default jumptable functions. */ diff --git a/libio/putc.c b/libio/putc.c index b591c5538b8..6e1fdeef3a2 100644 --- a/libio/putc.c +++ b/libio/putc.c @@ -25,6 +25,8 @@ _IO_putc (int c, _IO_FILE *fp) { int result; CHECK_FILE (fp, EOF); + if (!_IO_need_lock (fp)) + return _IO_putc_unlocked (c, fp); _IO_acquire_lock (fp); result = _IO_putc_unlocked (c, fp); _IO_release_lock (fp); diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c index 7a970ffc5bc..2f8ada34d60 100644 --- a/nptl/pthread_create.c +++ b/nptl/pthread_create.c @@ -32,6 +32,7 @@ #include #include #include +#include "libioP.h" #include @@ -756,6 +757,9 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr, collect_default_sched (pd); } + if (__glibc_unlikely (__nptl_nthreads == 1)) + _IO_enable_locks (); + /* Pass the descriptor to the caller. */ *newthread = (pthread_t) pd; diff --git a/sysdeps/pthread/flockfile.c b/sysdeps/pthread/flockfile.c index 7fe8e991616..a8e6c28ed94 100644 --- a/sysdeps/pthread/flockfile.c +++ b/sysdeps/pthread/flockfile.c @@ -25,6 +25,7 @@ void __flockfile (FILE *stream) { + stream->_flags2 |= _IO_FLAGS2_NEED_LOCK; _IO_lock_lock (*stream->_lock); } strong_alias (__flockfile, _IO_flockfile)